based on the raws it seems that most of the girls secretly have feelings for the MC but are unaware that he is already going out with someone. Wacky ecchi hi-jinks occur in later chapters resulting in the guy being in somewhat compromising positions with each of the girls (kinda like To Love-Ru) and leading to misunderstandings. But he is NOT cheating and the Girlfriend is understanding enough to see that, with her also taking part in the hi-jinks as well. If you're not into stuff like To Love-Ru, I advise you stop reading. The art is really good though.